1. Field of the Invention
This invention relates to a system for forming a magnetic film in a magnetic field and more particularly to a magnetic film forming system having a plurality of process chambers, and transport mechanisms for transporting substrates from one process chamber to another.
2. Description of the Related Art
A conventional inline film forming system is described with reference to FIG. 9. The inline film forming system in FIG. 9 comprises a substrate inlet chamber 2, three process chambers 1a, 1b, and 1c, and a substrate outlet chamber 3 which are linked in order. Sluice valves 8a, 8b, 8c, and 8d are disposed between each of the chambers. Each of the process chambers 1a, 1b, and 1c is provided with a device (not shown) for performing one process such as heating a substrate before film forming, sputtering film forming, ion beam sputtering film forming, or film forming by evaporation. A transport line 5 for transporting a substrate 101 is extended through the substrate inlet chamber 2, process chambers 1a, 1b, and 1c, and substrate outlet chamber 3.
The sequence for forming a film by using the system will be described. First, a substrate 101 on which a film is to be formed is fed into the inlet chamber 2, which is then evacuated by evacuation installation 9a. The process chambers 1a, 1b, and 1c, and the outlet chamber 3 are evacuated by evacuation installations 9b, 9b, 9d, and 9e respectively. After the inlet chamber 2 is evacuated, the separation valve 8a is opened and the transport line 5 is operated to transport the substrate 101 to the process chamber 1a, which has been already evacuated. In the process chamber 1a, predetermined steps such as heating the substrate before film formation and film formation are performed by the processing device installed in the chamber. After the predetermined steps are performed, the separation valve 8b is opened and the substrate 101 is transported to the following process chamber 1b over the transport line 5. Upon completion of processing the substrate 101 in the process chamber 1b, the substrate 101 is transported to the process chamber 1c for further processing. After predetermined processing in the process chamber 1c is complete, the substrate 101 is transported to the outlet chamber 3 from which it is removed. A large number of substrates 101 can be fed in sequence into the substrate inlet chamber 2 and through the process chambers 1a, 1b, and 1c one after another for processing.
In order, to form a film whose magnetic orientation is aligned, a film forming method in a magnetic field is used by which a film is formed while magnetic orientation of film particles is being aligned by applying a magnetic field. An example of the film forming system in the related art is given in "Journal of Vacuum Science & Technology A (Composition distribution and magnetic characteristics of sputtered Permalloy films with substrate angle)" second series volume 7, number 3, May/June 1989. This article describes a technique in which a permanent magnet is attached to a substrate holder which is fixed to a film forming system and a substrate is mounted on the substrate holder.
To form a magnetic film in a magnetic field by a conventional inline film forming system, magnetic field generation means is fixed outside or inside a process chamber and a magnetic field is applied to a space within the process chamber where a substrate is placed.
An example of a conventional inline system in which magnetic field generation means is attached outside a sputter film forming process chamber will be described with reference to FIG. 7. As shown here, Helmholtz magnetic coils 4a, 4b, 4c, and 4d are disposed outside a process chamber 1d which is provided with a magnetic target 3 and an RF power supply 2 for applying voltage to the magnetic target 3. The Helmholtz magnetic coils 4a, 4b, 4c, and 4d form a magnetic field 6 in a space where a substrate 101 is placed. The substrate 101 is supported by a transport line (not shown). Magnetic sputter particles sputtered from the magnetic target 3 are affected by the magnetic field 6 to form a film magnetically oriented on the substrate 101.
An example of a conventional inline system in which magnetic field generation means is attached inside a sputter film forming process chamber will be described with reference to FIG. 8. As shown here, permanent magnets 4e and 4f are disposed at places around a substrate 101 carried in a process chamber 1e. The permanent magnets 4e and 4f are supported by magnetic support means 7 fixed to the process chamber 1e. Since the permanent magnets 4e and 4f form a magnetic field 6 in a space where the substrate 101 is supported by a transport line (not shown), sputter particles sputtered from the magnetic target 3 are affected by the magnetic field 6 to form a film magnetically oriented on the substrate 101.
However, a conventional film forming system having such magnetic field generation means suffers from the problem that when a substrate is taken out from the film forming system after a film has been formed, it is placed out of the magnetic field of the magnetic field generation means. Thus, if the substrate is taken out from the film forming system in the state in which it is not completely cooled after the film has been formed, the magnetic orientation of the film is not aligned, there by degrading the magnetic characteristic. To prevent this inconvenience, the substrate must be left in the film forming system until it is completely cooled after film formation. It takes time until the substrate is completely cooled, substantially lowering the throughput of the system.
Forming a magnetic multilayer film by using the conventional inline system having such magnetic field generation means, suffers from the following problems:
(1) To form a multilayer film, a number of film forming process chambers which differ in film forming source must each be provided with magnetic field generation means. At the time, it is very difficult to completely match the various directions of magnetic fields applied to substrates by the magnetic field generation means in the process chambers. This causes the orientation of the magnetic film to vary from one layer to another, degrading the magnetic characteristic of the magnetic film. There are two main reasons why the directions of the magnetic fields in the process chambers cannot be matched are as follows. First, to completely match the directions of the magnetic fields generated by the magnetic field generation means in the film forming process chambers, the directions of coils and magnets must be matched completely. However, it is technically very difficult to completely match the directions of coils and magnets which are separated from each other and adjustment of the directions requires that the system be stopped over a long period of time. Second, when a substrate is transported, the substrate turns and its direction will vary.
(2) When the magnetic field generation means is installed outside each film forming process chamber, a magnetic field must be generated within the process chamber, thus a large magnetic field generation means needs to be installed, there by increasing costs.
(3) Process chambers must be located apart from each other to prevent magnetic fields generated by magnetic field generation means in the contiguous process chambers from affecting each other to become uneven magnetic fields. Thus, the line in the system is longer as compared with a normal inline system having no magnetic field generation means, leading to inconvenient installation of the former system.
(4) When a substrate is transported to the contiguous film forming process chamber after film formation, it is temporarily placed out of the magnetic field. Thus, if it is transported to the next process chamber in the state in which the substrate is not completely cooled after film formation, it is cooled out of the magnetic field, and so thus the magnetic orientation of the film is not aligned, this degrading the magnetic characteristic of the magnetic material. To prevent this inconvenience, the substrate must be left in the process chamber until it is completely cooled after film formation. It takes time to cool the substrate, which substantially lowers the throughput of the line.